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Home , Alnus oblongifolia, Arbutus arizonica, Chiricahua Mountains, Eysenhardtia orthocarpa, Haematoxylum brasiletto, Oak savanna

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Trees of the Northern and Sky Islands of Southwestern

Richard S. Felger1 and Matthew B. Johnson2

Abstract.-This report covers the naturally occurring montane flora of the northern Sierra Madre Occidental of eastern and western and the sky islands extending into southeastern and southwestern New . This flora is comprised of 233 in 130 genera and 61 families, which represents approximately 5 percent of the total flora of the . The region is a meeting place of the temperate North American and Neotropical tree floras with intrusions of Sonoran and at lower elevations. The legume (), (Fagaceae), and () families are the most diverse, and the (Quercus) and (Pinus) are the largest genera. This is the first comprehensive listing of the of the northern Sierra Madre Occidental. Extensive areas of tropical (TDF) cover the lower elevations of the southern part of the region in Sonora and Chihuahua and harbor 60 percent of the regional tree flora. Oak and pine-oak woodland occur at higher elevations and mixed forest at the highest elevations, and support 43, 33, and 11 percent respectively of the regional tree flora, The Madrean forest once stretched unbroken into the American but accelerating is leading to fragmentation of the keystone species populations,

INTRODUCTION We are including all of the tree species known to us in the montane at elevations above This publication covers the trees of the sky is­ the deserts and in the north, and above land mountains of southeastern~rizona, tropical thornscrub in the south. The northern sky southwestern , northeastern Sonora, islands, especially at higher elevations, have a and northwestern Chihuahua, and the contiguous continental and temperate makeup. Many north northern Sierra Madre Occidental in western Chi­ temperate tree species penetrate far southward in huahua and eastern Sonora. The northern limit of the interior of Mexico at intermediate or higher this bioregion is marked by the Pinalefto Moun­ elevations in areas such as the Central . tains (Mt. Graham) in Arizona. Out of practicality Fourteen percent of the tree flora, or 33 tree taxa we have set the southern limit of this study at the (species and a few subspecies or varieties) reach Sonora- border and adjacent mountains of their southern limits in the region (Table 1, p. 78- southwestern Chihuahua. The mountains just east 83). of the Cascada de Basaseachic in southern Chi­ Overall, the region is arid to semi-arid except huahua form the southeastern point, and the at the highest elevations. The lower elevations in Sierra de Alamos in southern Sonora marks the the northern part of the region are bounded by the southwestern point. The ranges in Ari­ on the western flanks and the Chi­ zona include the , Galiuro, Huachuca, huahuan Desert and grassland on the eastern Pinalefto, Rincon, Santa Catalina, Santa Rita flanks. The southern mountains, especially at mountains, and in New Mexico the Animas and lower and intermediate elevations, support tropi­ southern Peloncillo mountains. A land of ex­ cal and subtropical biota. This southern flora, in tremes, it is topographically and geologically southeastern Sonora and southwestern Chihua­ complex. hua, consists largely of a flora that is continuous with the American tropics. As one moves north­ ward through our region, there is a tendency 1Dry/ands Institute, Tucson, AZ. towards a reduction in stature and an attrition of 2Desert Legume Program, University' of Arizona, Tucson, AZ. tropical species and genera. Seventy-two percent

71 of the tree flora, or 164 species of southern or would not be surprising to find the flex and the tropical origin reach their northern limits in the two Prunus species in northern Sinaloa. A number region (Table 1; also see Felger et al., this volume). of others occur only in the southern part of our Nine families represented by trees here do region and in northern Sinaloa, e.g., Albizia si­ not extend farther north in western North Amer­ naloensis, Brongniartia alamosana, Diospyros ica, i.e., Bombacaceae, Clethraceae, sonorae, Opuntia thurberi var. alamosenses, O. Cochlospermaceae, Erythroxylaceae, Magno­ wilcoxii, Quercus albocincta, Q. tarahumara, and liaceae, Myrsinaceae, , Olacaceae, and Sabal uresana. In fact, the flora of northern Si­ Opiliaceae. naloa flora is not separable from that of southern The total annual generally de­ Sonora and southwestern Chihuahua (Gentry creases from south to north, but increases with 1946a, 1946b, 1982). elevation. Precipitation is largely bi-seasonal. The The characters, including size, that constitute -like, summer rainy season is most pro­ a "tree" are often highly subjective but useful for nounced and dependable towards the south, indicating trends, and important for considering while winter precipitation increases in importance keystone or -modifying organisms. The de­ northward. moisture is the principal limiting marcation between the larger and smaller factor in this dry region. The northward expan­ trees is especially subjective. We have chosen a sion of many of the more tropical or subtropical height of 5 m as the artificial limit between shrubs species is blocked by an invisible "frost-line" of and trees, and when in doubt have favored in­ freezing weather coupled with increasing aridity. cluding woody and excluding the more Frosts are infrequent or virtually absent towards herbaceous species with seasonal die-back. We the southern part of the region at lower to inter­ have also decided that if a plant is classified as a mediate elevations. Increasing aridity northward tree one should be able to climb up into it, or tends to raise the lower elevational limits of the theoretically climb it if the spines are removed, tropical/subtropical trees while the frost-line de­ without causing it to collapse. Many have a single scends in elevation. This results in narrowing trunk at least 10 cm in diameter at about 1 m elevational distributions or bands of tropical/ sub­ above ground level. Some species included in this tropical species northward and fragmentation of listing have multiple trunks arising at or near the frost-sensitive and -intolerant popUlations ground and could be classified as shrubs rather into specific microhabitats. There is often some­ than trees. In some cases a particular species may what of a paradox, because microhabitats with the be a across most of its distribution in the most favorable moisture conditions (riparian bot­ region, but in favorable such as moist tomlands and north-facing slopes) tend to tropical it may develop into a sizeable experience the most severe freezing temperatures Table 2.-Summary of tree species of the northern Sierra (see Burquez et al., in press). Madre Occidental and the Sky Islands including the seven The total flora for the region is estimated to largest families and five largest genera. include at least 4,000 species of vascular plants No. of No. of No. of (Felger et al., this volume). Within this rich flora families genera species we have documented 233 species of trees (Table 2 7 26 Dicotyledons 56 119 198 1), which represent about 5 percent of the total Monocotyledons 3 4 9 flora. These tree species are distributed in 130 Total 61 130 233 genera and 61 families (Table 2). In our opinion Families: this tree flora is approximately 95 percent com­ Fabaceae 23 36 plete, with additional records likely to be found in Fagaceae 1 21 the remote mountains and canyons in southwest­ Pinaceae 4 18 Moraceae 4 9 ern Chihuahua and adjacent Sonora. The largest Euphorbiaceae 7 8 families of trees are the legume (Fabaceae), oak Cupressaceae 3 8 (Fagaceae), and pine (Pinaceae) families, and the Burseraceae 1 8 Salicaceae 2 7 most diverse genera are the oaks (Quercus; fig. 1) Cactaceae 4 6 and pines (Pinus) (Table 2). There are about seven tree species and one va­ Largest genera: QuerclJs 21 riety endemic to the region: Fraxinus gooddingii, Pinus 12 flex rubra, Nolina matapensis, Opuntia th urberi Bursera 8 var. thurberi, Prunus gentryi, P. zinggii, Yucca Acacia 6 Ficus 6 schottii, and Y. grandiflora (Table 1). However, it Juniperus 5

72 Figure 1.- of nineteen species of Madrean and sky island oaks (Quercus): (a) Q. albocincta, cusi, encino roble, encino prieto, a Red (Black) Oak. (b) Q. arizonica, Arizona white oak, encino blanco. (c) Q. chihuahuensis, Chihuahua oak, encino blanco, encino chino, a White Oak. (d) Q. chryso/epis, live oak, an intermediate Oak. (e> Q. coccolobifolia, encino negro, a Red Oak. (1) Q. durifolia, a Red Oak. (g) O. emoryi, Emory oak, blackjack oak, bel/ota, a Red Oak. (h) O. gambelll, Gambel oak, Rocky Mountain white oak. (I) Q. gr;sea, / gray oak, a White Oak. (j) 0, hypo/eucoides, silverleaf oak, encino blanco, encino c%ra do, cusi, a Red Oak. v;. -I: (k) O. hypo/eucoides, the southern form, sO,metimes ~~~...J..,~. ~.. ~ J),~...... -:.' .. ~ known as Q. scytophylla Liebm. (I) O. mcvaughii, encino roble, a Red Oak. (m) O. oblongifol/a, Mexican blue oak, encino azul, a White Oak. en) O. rugosa, net- oak, a Red Oak. (0) O. sideroxy/a, encino prieto, a Red Oak. (p) Q. subspathulata, a White Oak. (q)Q. tarahumara, hand basin oak, encino cajete, a Red Oak. (r) Q. toumeyl, a ,\-".' . " ~ " White Oak. (s) Q. tubercu/afa, encino amarillo, a White I Oak. (t) Q. vlminea, willow leaf oak, saudllo, a Red Oak. I /' Drawings by MBJ.

73 tree (e.g., Aralia humilis and Stemmadenia ture used here results from our interpretation of tomentosa). Other species are shrubs at higher ele­ the taxonomic literature and our work on the flora vations and in the northern part of the region (due of the region. The major vegetation types of the to repeated freeze-damage or drought-stress) and region and their tree floras are briefly summa­ trees in the more tropical southern regions (e.g., rized below. Erythrina flabelliformis, FOllquieria macdougalii, and Lysiloma watsonil). TROPICAL DECIDUOUS FOREST The summary of information in Table 1 calls for some comment. In reality the vegetation is not Tropical deciduous forest (TDF) is charac­ as simple as the classification presented. Many teristic of the dry tropics worldwide. Increase in trees may extend into neighboring vegetation human population is leading to global devasta­ zones along riparian habitats or in other special tion of this habitat. De-forestation and the situations. Extraordinary "shifts" in vegetation resulting desertification has contributed to sub­ types occur on (Whitaker & Niering tropical belts of misery circling the globe. TDF is 1965) and hydrothermically altered (­ the least studied of the major vegetation types of berg 1982, Burquez et al. 1992). The size-classes in the world. Because it is hardly fashionable to save Table 1 refer to the larger trees within any given poorly-known, scrawny and often thorny trees in taxon across the entire region. Fire and human hot, uncomfortable climates, world conservation mischief have eliminated most of the largest trees efforts have largely overlooked TDE The magnifi­ from many regions. In certain situations many cent tropical deciduous forest of the northern common trees that are usually small or at most Sierra Madre Occidental is seriously threatened. medium-sized may develop into large trees, e.g., The TDF in Sonora and adjacent southwestern Lysiloma watsonii and Vitex mollis along the Rio Chihuahua is the dry, northern arm of the great Guajaray north of Alamos, and Quercus tarahu­ TDF swath which sweeps northward in western mara in the vicinity of Mulatos in east-central Mexico. Sonoran-Chihuahuan TDF is sandwiched Sonora. Perhaps the large number of extraordinar­ between tropical thornscrub at lower elevations to ily large trees in the Guarijio Indian region of the the west and the oak zone at higher elevations to Guajaray is related to local conservation or man­ the east. Northward, along the east side of the agement practices. Sonoran Desert, TDF merges into a kind of inland There are, or were, trees virtually everywhere subtropical thornscrub (Felger & Lowe 1976, Bur­ in the montane areas-most of the region is or quez et al. in press) which in turn merges into was forested. But man is the enemy vf the tree. desertscrub (Shreve 1951). Paul Martin and Chuck The are receding rapidly. Human popula­ Bowden referred to TDF in Sonora as the Secret tion in the region remained low and major roads Forest (Bowden et al. 1993). Howard Scott Gentry few until the middle or latter part of the twentieth (1942) called it the Short-tree Forest, and David century. Much diversity of near natural habitats Brown (1982) called it Sinaloan Deciduous Forest. remains, but assaults on trees are escalating. Ma­ Felger & Lowe (1976) and Burquez et al. (in press) jor threats include , logging, firewood call it tropical deciduous forest. In its natural con­ cutting, charcoal-making, dearing for , dition in Sonora, Chihuahua, and northern mining, urbanization, and replacement of the for­ Sinaloa, there is essentially 100 percent ground ests with buffelgrass (Pennisetum ciliare) at lower cover of forest often 10-15 m tall made up of trees elevations in the southern part of the region. of tropical affinity. This summary is largely derived from our Summers are long and hot and winters short study of the trees of Sonora which will be treated and mild. Freezing weather within the forest is in depth in a forthcoming book (Felger & Johnson rare and apparently most of the TDF species are in press). Selected references dealing with trees of highly frost-sensitive. May and June days grow our region or adjacent areas include Benson & hotter and hotter, building up to the beginning of Darrow (1981), Flora North America (1993), Gen­ the long-awaited summer rains. Afternoon douds try (1942), Hastings et aL (1972), Kearney & increase day by day, and finally, when the violent Peebles (1960), Little (1950), Marshall (1957), thunderstorms begin, the leafless trees and vines Mearns (1907), Pennington & Sarukhan (1968), and undergrowth burst forth in a blaze of green Powell (1988), Shreve (1951), Spellenberg et al. (in (Gentry 1942). The monsoon rains begin soon af­ prep.), Standley (1920-1926), Steinmann & Felger ter summer solstice, celebrated on June 24 as El (in prep.), Turner et al. (in press), Vines (1960), Dia de San Juan. The rains typically continue Wiggins (1964), and White (1948). The nomencla- through August and into early September. Some

74 trees, such as Bursera spp., Cochlospermum, • Lysiloma microphyllum Erythrina, Jatropha, Ipomoea, and Pseudobom­ • L. TIVatsonii bax, defoliate very soon after the rains cease. • Pachycereus pecten-aboriginum However, most of the trees defoliate more gradu­ • Pithecellobium leucospermum ally. Midwinter rains may delay leaf-fall of certain • Senna atomaria species. Drought-induced deciduating leaves pro­ • Stenocereus montanus duce a virtually unique but ephemeral display of • S. thurberi highly varied pastel colors (Bowden et aL 1993). • Tabebuia chrysantha Spring drought brings on final defoliation to most • T. impetiginosa of the TDF trees. As the weather turns hotter and • Wimmeria mexicana dryer from March and April to June, even the tree chollas (Opuntia thurben) and prickly pears (e.g., OAK WOODLAND O. wilcoxiJ) become flaccid and droopy from water loss. Cicadas call loudly and writers visiting Oak woodland vegetation is widely the Sonoran TDF during the height of the pre­ distributed at elevations above desert, grassland, summer drought tell of skeleton forests and the thornscrub, or tropical deciduous forest, but lack of greenery. It is awesome to witness the sud­ below pine-oak woodland or pine forest. The den transformation to luxuriant tropical green species composition and tree density in oak with the start of the summer monsoon. woodland changes both with elevation and Flowering trees can be found at virtually any latitude. Although these oak zones have been time of the year but there are some significant called Madrean Evergreen Woodland (Brown peaks of color display. Mid-winter brings the 1982), many of the oaks and associated species are amapas (Tabebuia spp.), the palo santo (Ipomoea drought-decid uous during the late spring dry arborescens), and then the echo (Pachycereus pec­ season. Autumn colors associated with falling ten-aboriginum). Later in spring the cuajilote leaves in temperate regions are seen in our region (Pseudobombax palmen) and rosa amarilla (Co­ during the pre-summer drought. chlospermum vitiiolium) bring forth floral Extensive areas in the northern part of the displays. When fallen leaves are dry and crackling region are dominated by open of underfoot in the searing pre-monsoon heat the Emory oak or bellota (Quercus emorYl). The hillsides blaze with the dark blue of gauyacan are harvested in considerable quantity in (Guaiacum coulterl) and rose-purple of nesco northern Sonora in early summer and sold (Lonchocarpus hermannii, = Willardia mexicana). locally. This is one of the few remaining These are just a few of the more conspicuous flow­ comlnercial, wild food harvests in the region. ering trees. By and large the timing of The acorns are eaten fresh and are often ripening and -fall coincides with the begin­ consumed in cantinas-the floors becoming ning of the summer rains. littered with the empty shells. Emory oak, Sixty percent (140 species) of the tree species Mexican blue oak (Q. oblongiiolia), and Arizona of the region occur in TDF. Legumes rule the oak ( Q. arizonica) are the most common tropical-derived TDF as well as the regional low-elevation oaks in the northern part of the thornscrub and Sonoran desertscrub. The our region. At lower elevations these oak zones fast-growing mauto (Lysiloma microphyllum) and border grassland or desertscrub. There is many other legumes account for the vast majority sometimes a broad between oak of the TDF vegetative cover. Biological diversity is woodland and grassland where the oaks become high. No single species or small number of species widely spaced and grasses predominate, Such dominates-the forest is shared by a horde of areas have been termed oak-grassland or species. Prominent arborescent members of TDF oak-. In mountains in southeastern and in our region include the following: east-central Sonora oak woodland sometimes • Bursera spp. occurs as islands on acidic; hydrothermically· • Caesalpinia platyloba altered soils within tropical deciduous forest, • Ceiba aesculiiolia The ecotone between these two plant • Conzattia m ultif]ora communities is often only a few meters. • Fouquieria macdougalii Oak woodland in southeastern Sonora and • brasiletto southwestern Chihuahua, called Oak Forest by • Ipomoea arborescens Gentry (1942), shows considerable tropical • Lonchocarpus hermmmii affinity, At its lower limits it borders tropical

75 deciduous forest. Their boundaries are often communities Douglas (Pseudotsuga menziesiJ) remarkably well defined, apparently maintained is often locally common in an otherwise pine­ by fire. Across the Rio Mayo and Rio Fuerte dominated forest, thus blurring the boundary mountain it is common to see low fires with mixed conifer forest. creeping almost harmlessly through dry grasses, At higher elevations within the pine-oak zones forbs, and leaf litter among the barren oaks in the pines become increasingly conspicuous and May and June. These fires destroy small TDF trees the tree density increases so that the vegetation and shrubs but not the oaks and their associated could be called forest rather than woodland. Pine vegetation. forest is characteristically dominated by one spe­ The southern oak woodland is host to a rich cies of pine, usually Arizona pine (Pinus array of subtropical or Mexican oak species. There ponderosa var. arizonica), ponderosa pine (P pon­ is considerable elevational and habitat zonation derosa var. scopulorum), or white pine (P. among the diverse oaks. Many of the oaks in strobi/ormis), with scattered individuals or small southeastern Sonora and nearby southwestern groups of oaks, especially Gambel oak (Q. gambe­ Chihuahua are strikingly large-leaved (e.g., the JiJ) and net-leaf oak (Q. rugosa). Gambel oak is the hand-basin oak, Q. tarahumara) as compared to only winter-deciduous oak in our region. Pine for.. those of the northern part of the region. The est is more widespread in Chihuahua and southern oaks often support tropical epiphytes than in Sonora. Ponderosa pine replaces such as bromeliads (Tillandsia spp.) and orchids Arizona pine at the higher elevations in Chihua­ (e.g., Encyclia microbulbon, LaeJia autumnalis, hua and on the northernmost sky islands, These and Oncidium cebolleta). closely-related pines can be found intermixed in the in southern Ari­ PINE-OAK WOODLAND zona. Mountains ranges to the south have only Arizona pine, while the ranges to the north have only ponderosa pine. Extensive areas of pine-oak woodland occur along the east side of the in western Chihuahua. Along the western slope of MIXED CONIFER FOREST the Sierra Madre Occidental the climate is gener­ ally somewhat wetter, with presumably milder Mixed conifer forest is restricted to the highest winter temperatures, resulting in a more diverse mountain tops. Winters are cold and summers flora with more tropical elements .. inel uding cool and moist. It is most extensive in the north­ pine (Pinus engelmanmi), Durango pine ern sky islands and at the highest elevations in (P. durangensis), egg-cone pine (P. oocarpa), pino Chihuahua. Southward in Sonora, mixed conifer chino (P. herrerae), and Mexican tropical-montane forest occurs in extremely limited areas on north­ oaks. Towards southeastern Sonora and adjacent facing slopes and riparian canyons on north Chihuahua the pine-oak woodland is floristically slopes. Northeastern Sonora and adjacent Chihua­ and structurally akin to the Mexican pine-oak hua support mixed conifer forests at elevations woodland of central and southern Mexico. mostly above 2135 m (7000 ft). Mixed conifer for­ Pine-oak woodland is continuous with oak est barely extends into southeastern Sonora from woodland at lower elevations. In pine-oak wood­ Chihuahua above 2100 m (6890 ft) in the upper land the pines form the overstory while the oaks reaches of the Rio Mayo . Because there generally form an understory. There are extensive are more extensive areas of higher elevation in areas of pine-oak woodland in the mountains of Chihuahua the mixed conifer forest is more com­ our region. Pine-oak woodland is included within mon there. the concept of Madrean Evergreen Woodland Three coniferous genera, Abies (fir), Pinus, (Brown 1982), and the pine forest has been called and Pseudotsuga (Douglas fir), define this vegeta­ Madrean Montane Conifer Forest (Brown 1982). tion. These trees are cOlnmercially valuable for For our purposes of this study it is not practical to lumber, Most of the old growth forest has been distinguish pine-oak woodland from pine forest. logged, but in some places it is recovering from Especially in the southern part of our region oaks extensive logging in the mid-twentieth century, are a major part of the forests containing pines. Most of the broadleaf (dieot) trees found here are The abundance of oaks may be in part a conse­ winter-deciduous, e.g., Gambel oak (Quercus quence of overharvesting of pines. However, gambeJiJ), capulin or wild cherry (Prunus serot­ especially in the northern part of the region a dis­ ina), ash (Fraxinus papillosa), aspen (Populus tinctive pine forest is distinguishable" In these tremuloides), and New Mexico locust (Robinia

76 neomexicana). Riparian canyons are shaded with Carnegie Institution of Washington, Publication 527, tall forests that may include big-tooth maple (Acer Washington, D. C. grandidentatum) and () Gentry, H.S. 1946a. Sierra Tacuichamona-a Sinaloa plant locale. Bulletin of the Torrey Botanical Club 73:356-362. sometimes towering to 20 meters or more in Gentry, H.s.1946b. Notes on the vegetation of Sierra Suro­ height. The two highest sky island peaks, the Pi­ tato in northern Sinaloa. Bulletin of the Torrey Botanical nalefto and in southeastern Club 73(5):451-462. Arizona, support spruce-fir forest (Picea and Gentry, H.S. 1982. Sinaloan deciduous forest. Desert Plants Abies) as do a few localities on cold, north-facing 4:73-77. slopes at the highest elevations in southwestern Goldberg, D.E. 1982. :the distribution of evergreen and de­ Chihuahua. ciduous trees relative to soil type: an example from the Sierra Madre, Mexico, and a general model. Ecology 63:942-951. ACKNOWLEDGMENTS Hastings, J .R., R.M. Turner, & D .K. Warren .1972. An atlas of some plant distributions in the Sonoran Desert. Techni~ We thank the Wallace Genetic Foundation for cal Reports on the and of arid supporting our research on the trees of northwest­ regions. University of Arizona, Institute of Atmos­ ern Mexico. We also thank Lucinda McDade and p heric Ph ysics. Kearney, T.H. & R.H. Peebles. 1960. Arizona Flora. 2nd the staff at the University of Arizona Herbarium edition with supplement by J.T. Howell & E. McClin­ for their assistance, and Dennis Breedlove, Al­ tock. U ni versi ty of California Press. Berkeley. berto Burquez, Mark A. Dinlmitt, Mark Fishbein, Little, E.L. 1950. Southwestern trees - a guide to the native George Ferguson, James Henrickson, Phil Jenkins, species of New Mexico and Arizona. Agricultural hand­ Angelina Martinez-Yrizar, Stephanie Meyer, Andy book no.9,GovemmentPrintingOffice,Washington, D.C. Sanders, Richard Spellenberg, Victor Steinmann, Marshall, J.T., Jr. 1957. Birds of Pine-Oak Woodland in Tom Van Devender, Michael Wilson, David Yet­ and Adjacent Mexico. Pacific Coast man, and many others for generous help with this Avifauna Number 22. Mearns, EA. 1907. Mammals of the Mexican Boundary of the tree flora. .United States National Museum Bulletin56. Pennington, T.D. & J. Sarukhan. 1968. Manual para la identificacion de campo de los principales arboles LITERATURE CITED tropicales de Mexico. Instituto Nacional de Investi­ gaciones Forestales, Secretaria de Agricultura y Benson, L. & R.A. Darrow. 1981. Trees and shrubs of the Ganaderia. Mexico, D.F. Southwestern deserts, 3rd. edition. The University of Powell, A.M. 1988. Trees & Shrubs of Trans-Pecos . Arizona Press, Tucson, Arizona." Big Bend Natural History Association. Big Bend Na­ Bowden, C., J.W. Dykinga, & P.S. Martin. 1993. The secret tional Park, Texas. forest. U ni versity of New Mexico Press. Albuq uerque. Shreve, F.1951. Vegetation of the Sonoran Desert. Carnegie Brown, D.E. (ed.). 1982. Biotic communities of the Ameri­ Institution of Washington Publication no. 591, Vol. I of can Southwest - United States and Mexico. Desert Shreve & I. L. Wiggins. Flora and Vegetation of the Plants 4:3-341. Sonoran Desert. Burquez, A., A. Martlnez-Yrfzar, & R.s. Felger. in press. Spellenberg, R., T. Lebgue, & R. Corral D. in prep. Annotated at the Southern Desert Edge in Sonora, checklist of the plants of the Parque Nacional de la Cas­ Mexico. IN: R. Robichaux, ed. Ecology and Conserva­ cada de Basaseachic, southwest Chihuahua, Mexico. tion of the Sonoran Desert Flora: a tribute to the desert Standley,P.C.1920-1926. Trees and shrubsofMexico.Contri­ laboratory. University of Arizona Press. butionsfrom the United States National Herbarium 23. Burquez,A.,A.Martinez-Yrizar, &PS.Martin. 1992. From the Steinmann, VW. & R.S. Felger. in prep. A synopsis of the high Sierra Madre to the coast: changes in vegetation Eup horbiaceae in Sonora, Mexico. along highway 16, Maycobo-. Pp. 239-252. IN: Turner, R.M., J .E. Bowers, & T.L. Burgess. In Press. Sonoran K.F. Clark, J. Roldan-Quintana, & R. Schmidt (eds.). Desert plants: an ecological atlas. University of Arizona Northern Sierra Madre Occidental Province, Mexico, Press. Tucson. guidebook. EI Paso Geological Society.EI Paso, TX. Vines, R.A. 1960. Trees, shrubs, and woody vines of the Felger, RS. & C.H. Lowe. 1976. The Island and Coastal Southwest. University of Texas Press. Austin. Vegetation and Flora of the , Mexico. White, S.s. 1948. The vegetation and flora of the region of Natural History Museum of Los Angeles County, Con­ the Rio de Bavispe in northeastern Sonora, Mexico" tribu tions in Science 285.59 pp . Lloydia 11:229-302. Felger, R.S. & M.B. Johnson. in press. Trees of Sonora, Whitaker, R.H. & W.A. Niering. 1965. Vegetation of the Mexico. Oxford University Press. New York. Santa Catalina Mountains, Arizona: a gradient analysis Flora of North America Editorial Committee .1993. Flora of ofthesouthslope.Ecology46:429-452. North America 2. Oxford U niversi ty Press. New York. Wiggins,I.L.1964.Floraofthe Sonoran Desert. p.189-1740.IN: Gentry,H.s.1942. Rio Mayo plants - a study of the flora and F. Shreve & I.L. Wiggins. Flora and Vegetation of the Sono­ vegetation of the valley of the Rio Mayo, Sonora. ranDesert,2vols.Stanford UniversityPress.Stanford.

77 Table 1.- Montane tree flora of the northern Sierra Madre Occidental and the Sky Islands.

Geographic distributions: G = ''General'' distributions, found both north and south of the region; T = "Tropical" or "southern" taxa at the northern limits of their geographic ranges; N = "Northern" taxa at the southern limits of their ranges; R = occuring elsewhere within approximately the same latitudes as our region; E = endemic to our region. Tree size classes: S = small trees, 5-8 m tall; M = medium-sized trees, 9-18 m; L = large trees, 19 or more m. Habitats: TO = tropical deciduous forest; OK = oak woodland; PN = pine-oak woodland or forest; MX = mixed conifer forest. Non-native species are Indicated with an asterisk (*).

G T N R E S M L TO OK: PN MX GYMNOSPERMS (CONIFERAE - )

CUPRESSACEAE - CYPRESS FAMILY Cupressus arizonica Greene var. arizonica G M L OK PN C. lusitanica Mill. T L OK PN MX Juniperus coahuilensis (Martinez) R.P. Adams G S OK PN J. deppeana Steud. G OK PN J. durangensis Martinez T S OK PN J. flaccida Schldl. var. flaccida T S OK PN J. scopulorum Sarg. N S PN Taxodium mucronatum Ten. T L TD

PINACEAE - PINE FAMILY Abies bifolia A. Murr. N L MX A. concolor (Gord. & Glend.) Hildebr. N L MX A. durangensis Martinez T L MX Martinez T L MX P. engelmannii Engelm. var. engelmannii N L MX Zucco T S OK PN P. douglasiana Martinez T L PN P. durangensis Martinez T L OK PN P. edulis Engelm. N S OK PN P. engelmannii Carr. T L OK PN P. herrerae Martinez T L PN P. leiophylla Schiede & Deppe var. chihuahuana (Engelm.) Shaw T L OK PN P. lumholtzii Robins. & Fern. T L PN P. maximinoi H.E. Moore T L PN P. oocarpa Schiede var. oocarpa T L PN P. ponderosa Laws. & C. Laws. var. arizonica (Englm.) Shaw T L PN MX P. ponderosa var. scopulorum Engelm. N L PN MX P. strobiformis Engelm. G L PN MX Pseudotsuga menziesii (Mirb.) Franco var. glauca (Mayr) Franco G L PN MX

MONOCOTYLEDO NS

AGAVACEAE - AGAVE FAMILY Yucca arizonica McKelv. N S OK Y. grandiflora Gentry E S OK Y. schottii Engelm. E S OK PN

ARECACEAE (PALMAE) - PALM FAMILY Brahea aculeata (Brandeg.) H.E. Moore T S TD OK B. dulcis (H.B.K.) Mart. T S (M) TD OK PN B. elegans (Becc.) H.E. Moore T S (M) TD B. nitida Andre T S (M) TD OK Sabal uresana Trel. T M TD OK

NOLINACEAE ~ BEAR-GRASS FAMILY Nolina matapensis Wiggins E S TD OK

DICOTYLEDONS

ACERACEAE - MAPLE FAMILY Acer glabrum Torr. N S MX A. grandidentatum Nutt. N L OK PN MX A. negundo l. N M PN MX

78 - DOGBANE FAMILY Plumeria rubra L. T S TD Stemmadenia tomentosa Greenm. var. palmeri (Rose & StandI.) Woodson T S (M) TD glabra (Cav.) Link T S TD

AQUIFOLIACEAE - HOLLY FAMILY lIex rubra S. Wats. E M OK PN MX I. tolucana Hemsl. T M PN MX

ARALIACEAE - GINSENG FAMILY Aralia humilis Cav. T S (M) TD OK PN Oreopanax peltatum Linden T S (M) TD OK PN

ASTERACEAE (COMPOSITAE) - ASTER OR COMPOSITE FAMILY Montanoa rosei Robins. & Greenm. T S TD Parthenium tomentosum DC. var. stramonium (Greene) Rollins T S TD OK

BETULACEAE - FAMILY (L.) Moench ssp. tenuifolia (Nutt.) Breit. N M MX A. oblongifolia Torr. N L OK PN MX Ostrya virginiana (P. MilL) C. Koch G L OK PN MX

BIGNONIACEAE - BIGNONIA FAMILY Chilopsis linearis (Cav.) Sweet ssp. arcuata (Fosberg) Henricks. N S OK Tabebuia chrysantha (Jacq.) Nichols. ssp. chrysantha T M (L) TO T. impetiginosa (A. DC.) Standi. T M (L) TO

BOMBACACEAE - SILK-COTION FAMILY Celba aesculifolia (H.B.K.) Britt. & Baker T M TO Pseudobombax palmeri (S. Wats.) Dugand T M TO BORAGINACEAE - BORAGE FAMILY Cordia sonorae Rose T S TO

BUDDLEJACEAE - BUTIERFLY-BUSH FAMILY Buddleja cordata H.B.K. var. cordata T S (M) PN B. parviflora H.B.K. T S OK PN

BURSERACEAE - FRANKINCENSE FAMILY Bursera arborea (Rose) Riley T L TO B. fagaroides (H.B.K.) EngL var. elongata McVaugh T S TO B. grandifolia (SchldL) Engl. T M TO B. lancifolia (Schldl.) Engl. T S TO B. laxiflora S. Wats. T S TO B. penicillata (DC.) Engl. T M TO B. simaruba (L.) Sarg. T L TO B. stenophylla Sprauge & Riley T M TO

CACTACEAE - CACTUS FAMILY Opuntia thurberi Engelm. var. thurberi E S TO O. thurberi var. alamosenses (Britt. & Rose) Bravo T S TO O. wilcoxii Britt. & Rose T S TD Pachycereus pecten-aboriginum (Engelm.) Britt. & Rose T S (M) TO Pilosocereus alensis Weber T S TO Stenocereus montanus (Britt. & Rose) Buxb. T S (M) TO S. thurberi (Engelm.) Buxb. T S (M) TO

CAPRIFOLIACEAE - HONEYSUCKLE FAMILY Sambucus mexican a Presl N S OK PN

CELASTRACEAE - STAFF-TREE FAMILY Wimmeria mexicana (DC.) Lundell T S TO

79 CLETHRACEAE - CLETHRA FAMILY Clethra mexicana DC. T M OK PN

COCHLOSPERMACEAE - COCHLOSPERMUM FAMILY Cochlospermum vitifolium (Willd.) K. Spreng. T M TD

CONVOLVULACEAE - MORNING-GLORY FAMILY Ipomoea arborescens (Humb. & Bonpl.) G. Don var. pachyleuta Gentry T S (M) TD (OK)

CORNACEAE ~ DOGWOOD FAMILY Cornus disciflora DC. T S OK PN

EBENACEAE - PERSIMMON FAMILY Diospyros sonorae StandI. T M TD

ERICACEAE - HEATH FAMILY arizonica (A. Gray) Sarg. T M (L) OK PN MX A. xalapensis Sarg. T M PN

ERYTHROXYLACEAE - COCA FAMILY Erythroxylum mexicanum H.B.K. T S TD

EUPHORBIACEAE - SPURGE FAMILY Croton ct. niveus Jacq. T S TD Drypetes gentryi Monach. T L TD Jatropha cordata (Ort.) Mull. Arg. T S TD Manihot aesculifolia (H.B.K.) Pohl T S TD Manihot sp. T S TD *Ricinus communis L. G S TD Sapium appendiculatum (Mull. Arg.) Pax & K. Hoffm. T S TD Sebastiana pavoniana (Mull. Arg.) Mull. Arg. T M TD

FABACEAE (LEGUMINOSAE) - LEGUME OR BEAN FAMILY:

CAESALPINIOIDEAE - SENNA SUBFAMILY Bauhinia pringlei S. Wats. T S TO Caesalpinia caladenia StandI. T S TD C. palmeri S. Wats. T S TD C. platyloba S. Wats. T S TD Cercidium praecox (Ruiz & Pav.) Harms ssp. praecox T S TD Conzattia multiflora B.L. Robins. T L TO Haematoxylum brasiletto Karst. T S (M) TD *Parkinsonia aculeata L. T M TD Senna atomaria (L.) Irwin & Barneby T S TD

MIMOSOIDEAE - MIMOSA SUBFAMILY Acacia pringlei Rose ssp. californica (Brandeg.) Lee, Seigler & Ebinger T S TD A. cochliacantha Wi lid . T S TO A. coulteri Benth. T S TO A. farnesiana (L.) Willd. T S TD A. occidentalis Rose T M TO A. pennatula (Cham. & Schldl.) Benth. T S OK PN Albizia sinaloensis Britt. & Rose T L TO Leucaena lanceolata S. Wats. T M TO *L. leucocephala (Lam.) de Wit T S TO Lysiloma microphyllum Benth. T M (L) TO L. watsonii Rose T M (L) TO OK Mimosa palmeri Rose T S TO *Pithecellobium dulce (Roxb.) Benth. T L TO P. leucospermum Brandeg. T S TO P. mexicanum Rose T M TO Prosopis glandulosa Torr. var. torreyana (l.D. Bens.) M.C. Johnst. G M TO P. velutina Woot. N M OK

80 PAPILIONOIOEAE - BEAN SUBFAMILY Brongniartia alamosana Rydb. T S TO Coursetia glandulosa A. Gray T S TO OK Oiphysa occidental is Rose T S TO O. suberosa S. Wats. T S TO OK Erythrina flabelliform is Kearney T S TO OK orthocarpa (A. Gray) S. Wats. G S TO OK Lonchocarpus hermannii Sousa T S TO Piscidia mollis Rose T M TO Platymiscium trifoliolata Benth. T M TO Robinia neomexicana A. Gray var. neomexicana N S OK PN MX

FAGACEAE - FAMILY Quercus albocincta Trel. T M OK PN Q. arizonica Sarg. G M OK PN Q. chihuahuensis Trel. T M OK PN Q. chrysolepis Liebm. N S OK Q. coccolobifolia Trel. T M OK PN Q. crassifolia Humb. & Bonpl. T M OK PN Q. durifolia Seemen T L OK PN Q. emoryi Torr. R M OK PN Q. gambelii Nutt N M PN MX Q. grisea Liebm. G M OK Q. hypoleucoides A. Camus T M (L) OK PN Q. mcvaughii Spellenb. M (L) OK PN MX Q. oblongifolia Torr. R M OK Q. perpallida Trel. T M OK Q. rugosa Nee G M OK PN Q. sideroxyla Humb. & Bonpl. T M OK PN Q. subspathulata Trel. T M PN

Q. tarahumara Spellenb. o Bacon & Breedl. T L PN Q. toumeyi Sarg. N S OK PN Q. tuberculata Liebm. T M (TO) OK PN Q. viminea Trel. T M (L) OK PN

FOUQUIERIACEAE - OCOTILLO FAMILY Fouquieria macdougalii Nash T S TO F. splendens Engelm. ssp. splendens G S OK

JUGLANOACEAE - FAMILY Juglans major (Torr.) Heller G M OK PN

LAURACEAE-LAURELFAMILY Cinnamomum sp. T L TO OK Persea podadenia Blake T L OK PN

MAGNOLIACEAE - MAGNOLIA FAMILY Magnolia pacifica Vazq. ssp. tarahumara Vazq. T L OK PN

MALPIGHIACEAE - MALPIGHIA FAMILY Bunchosia sonorensis Rose T S TO Malpighia umbellata Rose T S TO

MELIACEAE - CHINABERRY FAMILY Cedrela odorata L. T L TO Trichilia americana (Ses. & Mog.) T.O. Penn. T S TO T. hirta L. T S TO

MORACEAE - MULBERRY FAMILY Chlorophora tinctoria (L.) Benth. & Hook. f. T L TO Ficus cotinifolia H.B.K. T l TD F. insipida Willd. T l TO F. maxima Mill. T L TO F. pertusa L. 1, T L TO F. petiolaris H.B.K. T L TD (OK) F. trigonata L. T L TO Morus microphylla Bucki. N S OK PN Trophis racemosa (L.) Urban T l TO

81 MYRSINACEAE - MYRSINE FAMILY Ardisia revoluta H.B.K. T M TD Myrsine coriacea (Sw.) Roem. & Schult. T M OK PN

MYRTACEAE - MYRTLE FAMILY * guajava L. T S TD OK P. sartorianum (0. Berg) Ndzu. T M TD

NYCTAGINACEAE - FOUR-O'CLOCK FAMILY Pisonia capitata (S. Wats.) StandI. T S (M) (L) TD

OLACACEAE - OLAX FAMILY Schoepfia schreberi J.F. Gmelin T S TD

OLEACEAE - OLIVE FAMILY Fraxinus gooddingii Little E S OK F. papillosa Lingelsh. R M OK PN MX F. velutina Torr. G L OK PN

OPILIACEAE - FAMILY racemosa (DC.) StandI. T S TD

PLATANACEAE - PLANE-TREE FAMILY wrightii S. Wats. G L TD OK PN

POLYGONACEAE - BUCKWHEAT FAMILY Coccoloba goldmanii StandI. T S TD

RHAMNACEAE - BUCKTHORN FAMILY Colubrina triflora Brongn. T M TD Karwinskia humboldtiana (Zucc.) Roem. & Schult. T S TD Rhamnus crocea Nutt. N S OK R. cf. mucronata Schldl. T S OK PN Ziziphus amole (Ses. & Mo~.) M.C. Johnst. T S TD

ROSACEAE - ROSE FAMILY Prunus emarginata (Dougl.) D. Dietr. N S (M) PN MX P. gentryi StandI. E S PN P. serotina Ehrh. ssp. capuli (Cav.) McVaugh T M OK PN MX P. serotina ssp. virens (Woot. & StandI.) McVaugh N M OK PN P. zinggii StandI. E L TD OK californica (Torr.) Sarg. ssp. pauciflora (StandI.) Hess & Henricks. T S OK V. californica spp. californica N S OK

RUBIACEAE - MADDER FAMILY Cephalanthus salicifolius Humb. & Bonpl. G S TO OK Hamelia xorullensis H.B.K. T S TO Hintonia latiflora (Ses. & Mo~.) Bullock T S TO Randia echinocarpa Ses. & Mo~. T S (M) TO

RUTACEAE - RUE FAMILY *Casimiroa edulis Llave & Lex. T M TO Esenbeckia hartmanii Robins. & Fern. R S TO Ptelea augustifolia Benth. G S OK

SALICACEAE - WILLOW FAMILY Populus angustifolia James N L PN P. brandegeei Schneid. R L TO OK P. fremontii S. Wats. ssp. fremontii N L OK P. trem uloides Michx. N M PN MX Salix bondplandiana H.B.K. L TO OK S. gooddingii Ball N M (L) TO OK PN S. taxifolia H.B.K. T S OK SAPINOACEAE - SOAPBERRY FAMILY Oodonaea viscosa Jacq. G S TO OK drummondii Hook. & Arn. N S (M) OK S. saponaria L T M TO Thouinia acuminata S. Wats. T S TO T. villosa OC. T S TO

82 SAPOTACEAE - SAPOTE FAMILY Sideroxylon capiri (OC.) Pitt. ssp. tempisque (Pitt.) T.O. Penn. T L TO S. lanuginosum Michx. ssp. rigidum (A. Gray) T.O. Penn. N S OK S. persimile (Hemsl.) T.O. Penn. ssp. subsessiliflorum (Hemsl.) T.O. Penn. T L TO OK S. tepicense (StandI.) T.O. Penn. T L TO

SIMAROUBACEAE - SIMAROUBA FAMILY Alvaradoa amorphoides Liebm. T S TO OK

SOLANACEAE - NIGHTSHAOE FAMILY Cestrum lanatum Mart. & Gal. T S TO OK *Nicotiana glauca Graham G S TO OK PN Solanum erianthum O. Oon T S TO

STERCULIACEAE - STERCULIA FAMILY Guazuma ulmifolia Lam. T M TO

TAMARICACEAE - TAMARISK FAMILY *Tamarix ramosissima Ladeb G S TO

TILIACEAE - LlNOEN FAMILY Heliocarpus attenuatus S. Wats. T S TO OK H. palmeri S. Wats. T S TO OK Tilia floridana Small G M PN

THEOPHRASTACEAE - THEOPHRASTA FAMILY Jacquinia macrocarpa Cav. ssp. pungens (A. Gray) Stahl T S TO

ULMACEAE - ELM FAMILY Aphananthe monoica (Hemsl.) Leroy T L TO Celtis iguanea (Jacq.) Sarg. T S (M) TO C. reticulata Torr. N M TO OK *Ulmus pumila L. N S OK

URTICACEAE - NETTLE FAMILY Urera caracasana (Jacq.) Griseb. T S (M) TO OK

VERBENACEAE - VERVAIN FAMILY Lippia umbellata Cav. T S TO OK Vitex mollis H.B.K. T S (M) (L) TO V. pyramidata Robins. T S TO OK

ZYGOPHYLLACEAE - CALTROP FAMILY Guaiacum coulteri A. Gray T S TO

22 166 32 5 8 120 60 54 140 98 75 26

83